Apparatus for contacting solids with gaseous fluids



Nov. 5, 195'] B. E. ROETHELI 2,812,244

APPARATUS FOR CONTACTING- soLms WITH 'GASEOUS mums Original Filed Aug.26. 1950 Bfundfi. Qoefiheli Enveqbor OLL orneg United States PatentAPPARATUS FOR CONTACTING SOLIDS WITH GASEOUS FLUIDS Bruno E. Roetheli,Pntney, London, England, assignor to Esso Research and EngineeringCompany, a corporation of Delaware Original application August 26, 1950,Serial No. 181,659. Divided and this application September 1, 1955,Serial No. 536,243

6 Claims. (Cl. 23-288) This invention relates to contacting solidparticles with gaseous fluid and, more particularly, relates toapparatus for carrying out treatments and reactions in which highconcentrations of subdivided solids and relatively short contact orreaction times are used, such as the catalytic dehydrogenation ofhydrocarbons, thermal cracking of hydrocarbons to produce acetyleniccompounds, demethanation of ketones, etc.

This application is a division of application Serial No. 181,659, filedAugust 26, 1950, and now abandoned.

Prior to the present invention, it has been ditficult to carry outoperations in which high concentrations of solids and short contact orreaction times are used as, for example, in the catalyticdehydrogenation of butenes to produce butadiene. While the inventionwill be specifically described in connection with the catalyticdehydrogenation of butenes, it is to be understood that the inventionmay be used with other processes for treating hydrocarbons or otherorganic material or inorganic material.

In the catalytic dehydrogenation of butenes to produce butadiene, it isnecessary to expose butene a-t reaction temperature to a relativelylarge amount of catalyst and at the same time limit the time of contactof the butene with the catalyst a reaction temperature to a minimum tominimize side reactions or thermal cracking.

The fluidized solids type of reactor is useful in certain reactions inwhich high concentrations of subdivided solid particles are obtained byselecting low velocities of gaseous fiuid or reactant passing upwardlythrough the solids. However, if such a reactor were used in the catalytic dehydrogenation of butene on a commercial scale,.

the reactor would be quite large in cross-section with a very shallowdense phase of catalyst. To prevent excessive carry-over of catalystfrom the, reactor, it would be necessary to have a large settling zoneabove the dense phase in the reactor and this would result in too muchtime of contact or reaction time of the butenes or other reactants atthe high temperature. Attempts at ac'com-' plishing the separation ofsolids and gases immediately following the dense phase have led to theuse .of cyclone separators reached by the solids-in-gas suspension overan extended tortuous path in the form of pipes having large bendswhereby the contact time was extended substantially beyond the desiredmaximum of, say 2-3 secends.

The present invention overcomes the aforementioned difliculties andaifords various additional advantages as will appear from thedescription given hereinafter with reference to the accompanyingdrawing.

In accordance with the present invention, the subdivided solids arepassed, at the high rate required to establish the desired high density,under .the pseudo-hydrostatic pressure of a vertical column .of thesolids maintained in a readily flowing condition by the addition ofsmall amounts of an aeration gas, into the lower portion of an annularvertical reaction .zonesurrounding said column over its entire length,said reactio'nzon'e ice having a relatively low velocity lower portionand a upper portions not exceeding that desired for thetreatmentinvolved. The velocity diiferential within the successiveportions of the reaction zone is established by providing substantiallyless free cross-sectional area in the upper portion than in the lowerportion of the reaction zone.

The high velocity, relatively dilute, suspension of solids in gasiformmaterial is passed from the upper portion of the reaction zone inswirling motion directly into a low velocity zone in the form of aconfined free space located directly above, and in open connection with,the upper level of the solids feed column and at least partiallysurrounded by the upper portion of the reaction zone. As a result of theswirling motion and the drop in velocity, gas-solids separation takesplace in the free space above the solids feed column, separated solidsfalling into the feed column. The treated gasiform fluid now containingsolids in a substantially ineffective low concentration is removed fromthe free space at a relatively low velocity to be passed to furthergas-solids separation and product recovery. In this manner, extensivegas-solids contact in dilute low velocity phases prior to solidsseparation and in pipe bonds is substantially eliminated.

Suitable operating conditions may vary within wide ranges depending onthe treatment involved and the character of the solids used. Quitegenerally, it may be stated that the invention contemplates solidparticle sizes including particles of l to 200 microns diameter; solidsto gas feed ratios to the reaction zone of about 1 to 25 lbs. of solidsper cu. ft. of gas depending on the specific reaction and catalystactivity involved; phase densities in the low velocity portion of thereaction zone of about 6 to 35 lbs. per cu. ft. and of about 2 to 30 inthe high velocity portion when using superficial linear gas velocitiesof about 0.5 to 50 ft. per second, preferably 3 to 50 ft. per second, inthe reaction zone; apparent densities of the solids feed column of about20 to 50 lbs. per cu. ft; and a solids entrainment in the gaseousproducts removed from above the solids feed column of about 0.005 to 0.2lb. per cu. ft. or higher depending on the actual density of thecatalyst.

When the invention is applied to treatments or reactions requiringcontinuous solids regeneration, spent solids may be Withdrawn from thesolids feed column, subjected to regeneration and returned to thereaction zone together with the feed gases. Alternatively orsimultaneously, solids separated from the dilute suspension leaving thefree space above the solids feed column may be passed to regenerationand returned to the reaction zone together with the feed gases.

Having set forth its objects and general nature the invention will bebest understood from the more detailed description hereinafter in whichreference will be made to the drawing, the single figure of whichillustrates a preferred embodiment of the invention.

Referring now to the drawing, the apparatus illustrated comprises avertical substantially cylindrical vessel 1.0 open at the top and havinga closed conical bottom 12 provided with a plurality of oblong orifices14 extending over at least a major portion of the length of cone 12.Orifices 14 are preferably adjustable. Vessel 10 is surrounded by ajacket 16 having a generally similar outline as vessel 10, but over itsentire length a larger diameter than adjacent portions of vessel 10 sothat a vertical free space is formed between jacket 16 and vessel 10over the entire length of the latter. Jacket 16 extends upwardly beyondthe open top of vessel and ends in a rounded cone cover 18, fitting inpressure'tight connection around a vertical concentrical tube 20extending downwardly a substantial distance into the upper portion ofvessel 10. The diameter of tube 2%) is about /s /s of that of theportion of vessel It) penetrated by tube 20. The lower conical portionof jacket 16 is continued by a feed pipe 22. The lower conical portion30 of the space between vessel 10 and jacket 16 is separated from feedpipe 22 by a gas distributing means, such as a perforated grid 24.

Vessel 16 and jacket 16 are so shaped that the vertical annular spaceformed by the same has a lower portion 26 of relatively largecross-section and an upper portion 28 of relatively small cross-section.This may be accomplished as shown in the drawing by recessing vessel 10inwardly and/or expanding jacket 16 outwardly below the transition linebetween portions 26 and 28. The width of portion 26 may be about 2-10times that of portion 28. Portion 30 may have about the same width asportion 26. The lengths of portions 30, 26 and 28 may be chosen in anysuitable manner, for example in the.

approximate ratio of 1 :2:2, in the order named.

If desired, portion 26 and/or portion 28 may be so designed that theyare vertically moveable in a telescoping fashion to permit an adjustmentof the ratio of their lengths as determined by the conditions of thespecific reaction involved. Portions 26, 23 and 30 may also be made ofsubstantially equal cross-section in which case velocity differentialsmay be established by placing suitable fillers in the high velocitysections.

A plurality of vertical bafiies or vanes 32 are arranged immediatelyabove portion 28 within the free space between the upper portion ofjacket 16 and the middle section of tube 20, close to the Wall of jacket16, in such a manner that a violently swirling action is imparted to thegases entering space 34 from portion 23. Vanes 32 may have the form offiat or curved plates placed at an angle (less than a right angle) tothe flow of the gas-solids mixture leaving the high velocity zone. A gasbleed line 36 is provided in the lower portion of vessel 10 at a pointabove orifices 14, adapted to supply small amounts of an aeration gas tovessel 19. A solids withdrawal line 38 may be arranged in a lowerportion of vessel 10 to carry solids from vessel 10 to any point outsidejacket 16.

In operation, vessel 10 contains a bed M10 of subdivided contact solidsmaintained by aeration gas fed through line 36 in a readily flowingcondition and having a well defined upper level L10 just below the lowerend of tube 20. Solids flow under the pseudo-hydrostatic pressure ofmass M10 through orifices 14 into portion 30 of the annular space at arate controlled by adjustment of the variable orifices 14. The gas to betreated is admitted through line 22 and grid 24 at a rate adequate toform the desired solids density and to establish the desired contacttherein in portions 30 and 26 which represent the principal portions ofthe treatment or reaction zone proper. The relatively dense upflowingsuspension of solids-ingases then enters portion 28 wherein its velocityis greatly increased with a corresponding decrease in density. The highvelocity suspension discharged from portion 28 enters space 34 incentrifugal strongly swirling motion imparted by vanes 32 so that space34 acts as a cycloneatype of separator. Separated solids collect onlevel Lie to be recirculated to the annular treating space while treatedgases leave through tube 20 at a relatively low velocity not conduciveto excessive solids entrainment. Fresh solids may be supplied with thefeed gases through pipe 22,and spent solids may be withdrawn throughline 38 as desired. It will be readily appreciated that in this manner,any desired contact time and solids density may be maintained by merelyadjusting the gas feed rate and the opening of orifices 14 whileavoiding undesirable delays in the gas-solids contact as the result ofextended residence in dilute low velocity phases and/or in pipe bends.

The invention will be further illustrated by the following more specificexample wherein reference will be made to the dehydrogenation of butenesto butadiene. It will be understood, however, that the method andapparatus of the invention may be applied in a generally analogousmanner to other catalytic or non-catalytic contacting of solids withgases requiring high phase densities and short contact times.

The butenes to be dehydrogenated are passed through line 22 into thebottom portion 3%) of the reaction zone. For maximum production ofbutadienes the butene feed comprises butenes 1 and 2 of reasonably highpurity. Where the catalyst is deactivated by steam, the use of steamshould be avoided and a subatmospheric pressure is preferably used formaintaining a low partial pressure rather than steam, or inert diluentsmay be used to get low Cni partial pressure.

The butene feed may be preheated to a temperature of about 300-l090 F.,but this is not essential since with one type of catalyst the heat forthe process may be supplied from the combustion of carbonaceous matterin a regenerator (not shown). The catalyst may comprise any suitabledehydrogenation catalyst, such as oxides of (l) chromium or aluminum ormixtures thereof, (2) iron, magnesium, copper or potassium or mixturesthereof, (3) vanadium, tungsten or molybdenum or mixtures thereof, etc.Regenerated catalyst heated to about a temperature of l3G0-l500 F.,preferably about l400 F., may be supplied together with the butene.

For catalysts in groups (1) and (3) the regeneration is carried out withair and in the absence of steam. For catalysts in group (2) steam isused for regeneration for removing coke or carbonaceous material by thewater gas reaction. About 10-20 tools of superheated steam per mol offeed should be used for regeneration. The temperature duringregeneration with steam is about l200 F. to 1400 F. Heat in addition tothat supplied by catalyst in the reaction zone is preferably supplied bysuperheated steam heated to a temperature above about 1200 F. When usinga catalyst containing potassium, it may be desirable to add a potassiumcompound to replace the potassium lost during the process. Suitabledehydrogenating conditions to be maintained in portion 26 includetemperatures of about 800l500 F. and pressures of about up to p. s. i.g.

Where regeneration temperatures are much higher than the reactiontemperature, the butene feed may be heated to a lower temperature toavoid thermal cracking and when it is mixed with the regeneratedcatalyst at a higher temperature, the butene feed is raised to thecracking temperature almost instantaneously. Also the steam may beheated to temperatures higher than reaction tempera tures before beingintroduced into the reaction zone to supply heat to the butene feed.

The catalyst in bed M10 is preferably in finely divided or pulverizedform of a size between about 50 and 400 standard mesh. However,substantially coarser particles up to diameters of A3" or A may be used.The butene feed passing upwardly through the reaction zone maintains thecatalyst particles in a dry fluidized liquid-simulating condition. Whenusing a catalyst of about 100 to 400 standard mesh the dense fluidizedmixture in portions 30 and 26 of the reaction zone will have a densitybetween about 10 lbs. per cubic foot and 50 lbs. or more per cubic foot,depending on the rate of addition of catalyst to the reaction zonerelative to the vapor rate, and upon the physical characteristics of thecatalyst.

The velocity of the butene vapors passing up through portions 30, 26 and28 of the reaction zone may vary between about 3 ft. per second to 50ft. per second. When the catalyst used comprises chromia and alumina andthe velocity of the butene vapors in zone 26 is about 20 ft. per second,the density of the fluidized mixture in portion 26 of the reaction zonewill be about 30 lbs. per cubic foot when catalyst is added to thereaction amazes zone from vessel at the rate of about -20 lbs. for eachcubic foot of vapor introduced. At these conditions the gas velocity inzone 28 may be upwards of 50 ft. per second. Lower gas velocities withinthe range of 5-20 ft. per second may be used in portion 26 when thereaction zones are shortened correspondingly. The reaction time or timeof contact of the butene feed with the catalyst particles from thedistribution plate 24 to the separating space 34 may vary between about0.1 second to 10 seconds, preferably about 0.1 to 2.0 seconds.

From the above it will be seen that the butene feed passes through thereaction zone at a high velocity, and in order to maintain catalystwithin the reaction zone or vessel it is necessary to feed a largeamount of catalyst particles to the reaction zone. Part of this catalystis fed in the form of hot regenerated catalyst particles. The majorportion is supplied by recirculation from the separating space 34through the catalyst column of bed M10 in vessel 10. As a result of theintimate heat exchange between bed M10 and the annular reaction zone,the catalyst in bed M10 has approximately the same temperature as thereaction zone whereby the heat economy of the system is greatly aided.Due to the high velocity of the vapors and to the feeding of the largeamount of catalyst particles to the reactionzone, the reaction Zone iscompletely flooded with catalyst in the dense phase of zones 30 and 26and the gaseous products passing overhead through these zones are in adense phase or mixture. Zone 28 is really an overflow pipe whichfacilitates more speedy removal of the dense phase mixture from the topportion of the reaction zone 26.

Catalyst separated in space 34 is collected on level L10 substantiallyat the rate at which catalyst is withdrawn through orifices 14. At theconditions of the present example, bed M10 may have a density of about40-50 lbs. per cu. ft. About 2-10 lbs. of superheated steam per sq. footof vessel area per hour may be injected through line 36 for aeration tomaintain bed M10 at this density and in free-flowing condition.

Gaseous reaction products leaving space 34 through tube may be quenchedto a temperature of about 500-l000 F. by injecting water or any otherconventional quenching medium, preferably after a secondary stage ofgas-solids separation (not shown). The reaction products in gaseous formleaving the last-mentioned separating means are passed to any suitableequipment for recovering desired products. Where butadiene is to berecovered, the reaction products are treated with a solvent which isselective for butadiene and the butadiene is then separated from thesolvent. Catalyst separated outside the unit shown may be returned toline 22 or to the regeneration stage. An amount ofabout 1-10% ofcirculating catalyst may be withdrawn through line 38 and passed to theregenerator to be returned therefrom via line 22 at substantially thesame rate, as indicated above.

During regeneration which may be carried out in any conventionalfluid-type of operation, the temperature is maintained between about1000 and 1500 F. As the regeneration reaction is exothermic when usingair, the temperature during regeneration must be controlled to preventdeactivation of the catalyst. This may be accomplished by inserting anindirect heat exchange coil in the dense fluidized phase of theregenerator or a portion of the regenerated catalyst may be withdrawnfrom the dense phase, cooled and returned to the regeneration zone allin a manner known per se. Other ways of controlling the temperature inthe regeneration zone may be used. If insuflicient combustible materialis deposited on the particles to satisfy the heat requirements,extraneous fuel may be injected into the regenerating vessel to supplythe additional heat by combustion.

When regenerating with steam, the steam is heated to a highertemperature than reaction temperature and in addition to steam fuel maybe burned in the regeneration zone to supply the heat necessary to raisethe temperature of the catalyst particles to above reaction temperaturein the reactor.

The present invention may also be used with non-catalytic solidparticles where the particles are used primarily for controlling thetemperature in the reaction zone by heating or cooling as the case maybe. The invention may be used in all cases where large amounts of solidparticles are to be maintained in a treating zone, While the particlesare being continuously removed therefrom, and where the gaseous fluidpasses through the treating zone at a relatively high velocity or wherethe time of contact between the solid particles and gaseous fluid in thetreating zone is exceedingly short.

While one form of apparatus has been shown and conditions for onecatalytic reaction, namely, catalytic dehydrogenation of butenes toproduce butadiene have been given, it is to be understood that these areby Way of example only and various changes and modifications may be madeWithout departing from the spirit of the invention.

What is claimed is:

1. Apparatus for contacting gaseous fluids with subdivided solids usinglarge amounts of solids and short contact times, which comprises avertical substantially cylindrical vessel open at the top, said vesselhaving a closed inverted conical bottom provided with a plurality ofoblong orifices extending over a substantial portion of the length ofsaid inverted conical bottom, a jacket surrounding said vessel over itsentire length in a spaced relationship to define a vertical annularspace of width substantially smaller than the diameter of said vessel,said jacket being closed at top and bottom and extending upwardly beyondthe open end of said vessel to define a confined space Within saidjacket above said vessel, the width of said annular space being 2 to 10times greater in its lower portion than in its upper portion, thelengths of the lower and upper portions of said annular space being in aratio between about 1:1 and 3 :2, a gas feed pipe leading into thebottom of said jacket, separating means communicating with the upperportion of said annular space and adapted to rapidly separate subdividedsolids from gaseous fluid and to return the separated solids to saidcylindrical vessel, and a tube communicating with said separating meansand adapted for removal of gaseous fluid therefrom.

2. The apparatus of claim 1 which comprises a gas feed line leading intoa lower portion of said vessel, and wherein said separating means is aplurality of vanes arranged in said confined space adjacent to saidjacket and annular space.

3. The apparatus of claim 1 in which said orifices are adjustable. 4.The apparatus of claim 1 which comprises a pipe connecting the bottom ofsaid vessel to the outside, said last-mentioned pipe being adapted tocarry subdivided aerated solids from said vessel to the outside.

5. The apparatus of claim 1 which comprises a perforated horizontal gridseparating the bottom of said annular space from said gas feed pipe.

6. The apparatus of claim 1 in which the diameter of said vertical tubeis about /s /s of that of the upper portion of said vessel.

. References Cited in the file of this patent UNITED STATES PATENTS

1. APPARATUS FOR CONTACTING GASEOUS FLUIDS WITH SUBDIVIDED SOLIDS USINGLARGE AMOUNTS OF SOLIDS AND SHORT CONTACT TIMES, WHICH COMPRISES AVERTICAL SUBSTANTIALLY